Sheet stretcher



S. E. WELLS SHEET STRETCHER Aug. 4, 1959 Filed July 15, 1957 2 Sheets-Skeet 1 mm :1! IE! on 7////////////// M g INVENTOR Sheldon E.We| Is mm on M//////// mm Arrow Aug'. 4, 1959 Filed July 15, 1957 s. E. WELLS SHEET STRETCHER 2 Sheets-Sheet 2 POWER SOURCE INVENTOR. Sheldon E.We| ls ATTORNEY Unite States Patent SHEET STRETCHER Sheldon Earl Wells, Youngstown, Ohio, assignor to Lombard Corporation, Youngstown, Ohio, a corporation of Ohio Application July 15, 1957, Serial No. 671,910

6 Claims. (Cl. 153-35) This invention relates to metal sheet or strip processing apparatus and more particularly to a sheet stretcher capable of producing a transition in the stress pattern across the sheet width.

Sheet steel is generally classified into two grades of flatness. In one of these, called commercial flatness, the sheets are intended to be subsequently worked; and, hence, the original flatness does not have much effect on the finished product. In the other, called stretcher level flatness, the sheets are used in applications where little subsequent forming is done on the sheet and the finished product is desired flat and free from buckles.

Commercial flatness can ordinarily be produced on a roller leveler or cold rolls, but where it is required that sheets be very flat, resort must be had to stretcher leveling. In the stretcher leveling operation, sheets are gripped at each end, usually by jaws which are forced apart slowly by hydraulic pressure. The effect produced is actually one of stretching the sheet gradually, taking up all the slack which may exist in the form of waves or buckles, and continuing until the sheet is stretched taut and its shape is practically a flat plane. Theoretically, the stretching proceeds past the elastic limit of the metal so that it will not spring back into its original shape but will spring back uniformly across its full width and remain flat. This means that the sheet takes a permanent set in its flat condition, which shape is not materially altered when stretching is stopped and the sheet removed from the jaws.

' In most prior art stretchers difiiculty was encountered in obtaining perfect gripping of the ends of the sheet. Slippage inthe gripper jaws will produce different unit stresses in different parts of the sheet. If this slippage is high enough so that stretching is not substantially uniform in all parts of the sheet, varying amounts of elastic contraction will result upon release of the load, which in turn produces nonflatness. It has been found, for example, that the jaws of most stretchers will grip the edges of the sheet more securely than the central region. This results in a condition of waves or buckles in the central part of the sheet. Conventional jaw-type stretchers also tend to produce. excessive stress concentrations 'where the jaws bite the sheet; and for high tensile steel, such stress concentrations can not be tolerated since they produce fracture due to the ultimate stress being reached in one region of the sheet prior to reaching the yield point in the remaining sections of the sheet.

It is a primary object of this invention to provide a sheet stretcher which produces a uniformly level finished product, thereby overcoming the disadvantages of previous stretchers.

More specifically, an object of the invention is to provide a sheet stretcher in which the unit stress in all parts of the sheet may be made uniform.

A furtherobjcct of the invention is to provide means for facilitating easy loading of a workpiece into the gripper jaws of a sheet stretcher.

A still further object of the invention is to provide a sheet stretcher in which any desired unit stress variation may be produced in different sections of a Workplece.

The above and other objects and features of the invention will become apparent from the following detailed description taken in connection with the accompanying drawings which form a part of this specification and in which:

Figure 1 is a broken-away elevation view of the invention showing the stretcher in idle position prior to initiation of a stretch cycle;

Figure 2 is a broken-away elevation view, similar to Figure 1, but showing the stretcher in position to begin a stretch operation;

Figure 3 shows the action of the stretcher during a stretch operation;

Figure 4 is an end view of the roll of Figure 5 showing the mechanism for clamping the opposite ends of a workpiece which is to be stretched in the apparatus of Figures 13 Figure 5 is a perspective view of one of the two rolls used in the apparatus shown in Figures 13; and

Figure 6 is a schematic diagram of the hydraulic and electrical control systems for the invention.

Referring to Figures 13, the stretcher of the present invention comprises a stretcher bed or base 10 having a pair of side panels extending upwardly and along its long transverse sides. In the broken-away elevation views of Figures 1-3, only the rear side panel 12 is shown, the other panel being located directly in front of the first. A centrally located plate 14- rests on the top edges of the two side panels to form a table for supporting a workpiece or sheet 16 during a loading operation. Each of the side panels has a portion 18 extending upwardly at the left end of the stretcher for supporting an axle 20 which, in turn, carries a first rotatable stretcher roll 22. Keyed to one end of axle 20 is a segmented pinion 24 which engages a rack 25 reciprocably mounted on a guideway 26, the arrangement being such that as the rack 25 moves forwards or backwards, the pinion 24, axle 20 and roll 22 are forced to rotate in one direction or the other. Motive power for the rack and pinion arrangement is provided by a double acting hydraulic cylinder 28, substantially as shown.

At the opposite end of the bed 10 is a track structure 30 extending generally perpendicular to the axis of roll 22." Reciprocably mounted on this track structure is a carriage 32 which can move back and forth between a first position outwardly of the plate 14 and a second position where it engages a stop 34 extending upwardly from the track structure adjacent plate 14. The carriage 32 may be forced to the right as shown in Figures 1-3 by a singleacting hydraulic cylinder 36.

Carriage 32 is provided with two side panels which extend upwardly along its long transverse sides. In Figures 13 only the back panel 38 is shown. Extending between these panels is an axle 40 which carries a second rotatable stretcher roll 42. Axle 40, like axle 20, has a segmented pinion 44, keyed thereto which cooperates with a rack 46, reciprocable on a guideway formed on the upper surface of carriage '52. Rack 46 is forced to reciprocate on its guideway to thereby rotate pinion 44 and roll 42 by the action of a double-acting hydraulic cylinder 48.

Formed in the periphery of each of the rolls 22 and 42 is a slot 50 extending parallel to the axis of the roll.

'Each of the slots 50 is adapted to receive an end of of roll 22 is also provided with a second slot 54, spaced substantially degrees from the slot 50. When the roll 22 is rotated substantially 90 degrees counter-clockwise from the position shown in Figure 1, the slot 54 is in alignment with a lock bar 53 which may be selectively forced into slot 50 by double-acting hydraulic cylinder 55. Obviously, when the lock bar 53 extends into slot 54, the roll 22 is restrained against further rotation.

The details of the clamping devices'52 are shown in Figure 4. As shown, each clamping device comprises a rotatable shaft 56 extending parallel to the axis of the roll on the inside surface of the slot 50. Suitable journal bearings, not shown, may be employed to secure shaft 56 to the inner surface of slot 50. Keyed to the shaft 56 is a cam 58 which may extend along the entire length of the shaft or may be segmented, depending upon requirements. Keyed to each end of the shaft 56 is a crank arm 60 having its outer extremity pivotally connected to the piston rod of a double-acting hydraulic cylinder 62. The end of cylinder 62 opposite the piston rod is pivotally connected at 64 to the side of the roll. As will be understood, the cylinders 62 at each end of the roll may be pressurized to rotate cam 58 from a gripping position to a release position, and vice versa.

Successive phases of the stretch cycle are shown in Figures 1, 2 and 3. In Figure l the workpiece 16 is shown on the plate 14 with its opposite ends extending into the slots 50 in each of the rolls 22 and 42. To accommodate difterent sheet lengths, the cylinder 36 may be pressurized to move carriage 32 to the right and thereby vary the spacing between rolls 22 and 42. After the ends of the sheet 16 are clamped by devices 52, cylinder 28 is pressurized to move rack 25' to the right while cylinder 48 is simultaneously pressurized to move rack 46 to the left. This has the effect of rotating roll 22 counter-clockwise while roll 42 is rotated clockwise. After cylinder 28 has rotated roll 22 through 90 degrees, slot 54 will be in alignment with lock bar 52, whereupon cylinder 55 is pressurized to force the lock bar into the slot and restrain further rotation of roll 22.

As rolls 22 and 42 rotate in opposite directions, slots 50 and, consequently, the workpiece 16 are elevated above plate 14 and into the position shown in Figure 2. The slots 50 tend to move apart during this process, thereby creating tension in the workpiece 16 which drags carriage 32 to the left and into engagement with stop 34. This condition is shown in Figure 2. When the carriage 32 thus engages stop 34, a limit switch, not shown in Figures 1-3, is tripped which causes a hydraulic system to apply a much higher pressure to cylinder 48. Any further rotation of roll 42 under this increased pressure stretches the workpiece 16 until it is perfectly flat and free from buckles. In Figure 3 the system is shown after the stretching operation during which the workpiece 16 is pulled taut by further clockwise rotation of the roll 42 from its position shown in Figure 2.

As is explained in the introductory part of this specification, previous stretches could not produce a uniform unit stress pattern across the width of the workpiece because of slippage in the stretcher jaws. That is, the jaws would grip the ends of the workpiece more securely than its central portion, thereby causing a greater unit stress at the edges. This condition is prevented in the present invention by crowning one or both of the rolls as shown in Figure 5. It will be obvious that since the diameter of the roll is greater at its center than at its ends, the central region of the workpiece will be subjected to a greater unit stress than the ends, neglecting any slippage in the devices 52. However, since slippage inherently occurs in this central region, the unit stress across the workpiece tends to level out. Obviously, the shape of the rolls may be altered to produce any desired stress transition across the width of the workpiece. If, for example, the rolls are made concave rather than convex as shown in Figure 5, a much greater unit stress will be produced at the edges than at the center.

One type of hydraulic system and control for the present invention is shown in Figure 6. It comprises a pair of electric motors 70 and 72 which derive their power from a power source 74. As will be apparent, both motors 70 and 72 run continuously.

Motor 70 drives a low pressure pump 78; whereas motor 72 drives a similar high pressure pump 80, the inlet ports of both of these pumps being connected to a reservoir 82 through conduit 84. Relief valves 86 and 88 connect the outlet ports of pumps 78 and 80, respectively, to reservoir 82 to prevent excessive pressure from damaging any parts of the system. The outlet ports of pumps 78 and are also connected to a high pressure conduit 90 through check valves 92 and 94, respectively. A low pressure line 96 is connected to reservoir 82, substantially as shown. Normally, the outlet of high pressure pump 80 will be bypassed to the reservoir through an open valve 81. Valve 81 is closed when a source of electrical energy, such as battery 83, is connected to valve-operating solenoid through the contacts of a limit switch '76 located at the left end of carriage 32. This limit switch will be closed when, and only when, the carriage engages stop 34 shown in Figures 13.

It will be apparent from the drawing that cylinder 55 is controlled by a valve 98, cylinder 28 is controlled by valve 100, cylinder 36 is controlled by valve 102, and the main power cylinder 48 is controlled by valve 104. Valve 98 is biased to normally connect the high pressure conduit to the right side of cylinder 55 through conduit 106, and the left side of this same cylinder to low pressure conduit 96 through conduit 108, thereby forcing the lock bar 53 into its retracted position. In a similar manner, valve 100 is biased to connect high pressure conduit 90 to the right side of cylinder 28 through conduit 110, and the low pressure conduit 96 to the left side of the same cylinder through conduit 112, thereby forcing rack 25 to the left whereby slot 50 is in the position shown. Valve 102 is biased to connect the left side of cylinder 36 to low pressure conduit 96 through conduit 114 whereby the carriage 32 is free to move to the left. Finally, valve 104 is biased to connect the high pressure conduit 90 to the left side of cylinder 48 via conduit 116 and the right side of this same cylinder to low pressure conduit 96 through conduit 118, thereby forcing rack 46 to the left so that the slot 50 in roll 42 is in the position shown. Under the conditions just described, a workpiece may be loaded into the slots 50.

Each of the valves 98, 100, 102 and 104 is controlled by an associated solenoid which is energized from a source of voltage, such as battery 120. When an operator-operated switch 122 is closed, the solenoids 124 and 126 for valves 100 and 104, respectively, will be connected to battery 120, thereby reversing the connection of high and low pressure conduits 90 and 96 to cylinders 28 and 48. Solenoid 128 for valve 98, however, will not be energized to reverse the connections to cylinder 55 until limit switch 130 is closed, indicating that roll 22 has rotated 90 degrees counter-clockwise so that slot 54 is in alignment with lock bar 53. Solenoid 132 for valve 102 will not be energized to pressurize the left side of cylinder 36 until an operator-operated switch 134 is closed.

In operation, the valves 81, 98, 100, 102 and 104 will normally be in the positions shown. Low pressure pump '78 will deliver fluid through check valve 92 and close check valve 94 since the output of high pressure pump 80 is connected to reservoir 82 through valve 81 at this time. Under these conditions, rolls 22 and 42 will be rotated so that the slots 50 face each other, thereby facilitating loading of a workpiece into the stretcher. After the workpiece is clamped by gripping devices 52, not shown in Figure 6, the operator will depress switch 122, thereby energizing solenoids 124 and 126. This reverses the positions of valves 100 and 104, so that now the left and right sides of cylinders 28 and 48, respectively, are connected to the high pressure conduit 90. Thus, rolls 22 and 42 rotates in opposite directions, elevating the workpiece and shifting the carriage 32 to the left until it engages stop 34 and limit switch 76. Before carriage 32 engages limit switch 76, however, rack 25 will engage limit switch 130, thereby energizing relay 128 and causing cylinder 55, through valve 98, to force lock bar 53 into slot 54 which has by this time rotated 90 degrees.

.When lock bar 53 is forced into slot 54 and limit switch 76 is tripped, battery 83 is connected to solenoid 85 which will then close valve 81. Since the pressure from pump 80 is much greater than that from pump 78, it will open check valve 94, close check valve 92 and apply a higher pressure to the right side of cylinder 48. The roll 42 is thereby forced to rotate further in a clockwise direction to stretch the workpiece.

At the completion of a stretching operation, an operator-operated switch 150 is first opened to disconnect the battery 83 from solenoid 85, thereby opening valve 81 and decreasing the pressure in conduit 90. Thereafter, switch 122 is opened. This breaks the circuit to solenoid 128 so that valve 98 is returned to its original position and lock bar 53 is withdrawn from slot 54. Opening switch 122 also deenergizes solenoids 124 and 126 so that cylinders 28 and 48 are pressurized to rotate rolls 22 and 42 to their original positions. At the same time, the operator closes switch 134 to energize relay 132 and connect the left side of cylinder 36 to the high pressure line 90. Cylinder 36 thus forces carriage 32 back to its original position. The cycle is then completed. At any time after the stretch operation, the workpiece may be released from slots 50 by manipulation of gripping device 52.

Although the invention has been shown in connection with a certain specific embodiment, it will be readily apparent to those skilled in the art that various changes in form and arrangement of parts may be made to suit requirements without departing from the spirit and scope of the invention.

I claim as my invention:

1. A stretcher for metal strip comprising, in combination, a base member, a first cylindrical roll rotatable about an axis which is fixedly positioned at one end of said base member, a carriage mounted at the other end of said base member, said carriage being freely movable in a direction which is perpendicular to said axis, a stop member for limiting movement of said carriage toward said first roll, a second cylindrical roll mounted on said carriage and rotatable about an axis which is substantially parallel to said first-mentioned axis, means on the outer peripheries of said rolls for clamping the opposite ends of a strip which is to be stretched, and means for rotating said rolls in opposite directions about their respective axes with'the ends of the strip clamped thereon whereby said carriage is moved into engagement with said stop member, whereupon further rotation of at least one of said rolls will cause stretching to occur in said sheet.

2. A stretcher for metal strip comprising, in combination, a base member, a cylindrical roll rotatable about an axis which is fixedly positioned at one end of said base member, a track structure on said base member extending in a direction which is generally perpendicular to the axis of said cylindrical roll, a carriage mounted for longitudinal movement along said track structure, a stop for limiting movement of said carriage toward said roll, a second cylindrical roll mounted on said carriage and rotatable about an axis which is substantially parallel to said first-mentioned axis, cam means on the outer peripheries of said rolls for clamping the opposite ends of a workpiece which is to be stretched, means for rotating said rolls in opposite directions after a workpiece is clamped by said cam means whereby said carriage is moved along said track structure toward said stop, and means for preventing rotation of the first-mentioned roll when the carriage engages said stop.

3. A stretcher for metal strip comprising, in combination, a first cylinder rotatable about an axis which is fixed in one position, a second cylinder rotatable about an axis which is substantially parallel to said first-mentioned axis, said-second cylinder and the axis about which it rotates being freely movable in a direction which is substantially perpendicular to said first-mentioned axis, means for limiting movement of said second cylinder toward said first cylinder, means on the outer peripheries of said cylinders for clamping the opposite ends of a workpiece which is to be stretched, and means for rotating said cylinders in opposite directions whereby said second cylinder will move toward the first cylinder until it engages said means to limit movement, whereupon the workpiece will be elevated to a position where its plane is tangential to the peripheries of said cylinders and further rotation of at least one of said cylinders will cause stretching to occur in said workpiece.

4. A stretcher for metal strip comprising, in combination, a first roll rotatable about an axis which is fixed in one position, said first roll having a cross sectional area greater at the center of its longitudinal length than at the ends thereof, a second roll rotatable about an axis which is substantially parallel to said first-mentioned axis, said second roll also having a cross sectional area greater at the center of its longitudinal length than at the ends thereof to match the cross sectional area of said first roll, said second roll and the axis about which it rotates being freely movable in a direction which is substantially perpendicular to said first-mentioned axis, a stop member for limiting movement of said second roll toward said first roll, means on the outer peripheries of said rolls for clamping a workpiece which is to be stretched, and means for rotating said rolls in opposite directions with the workpiece clamped thereon whereby said freely movable second roll is forced to move toward said first roll until its movement is prevented by said stop member, whereupon the workpiece will be elevated to a position where its plane is tangential to the peripheries of said rolls and further rotation of at least one of said rolls will cause stretching to occur in said workpiece.

5. A stretcher for flat workpieces comprising, in combination, .a base member having a substantially flat table portion, a first roll rotatable about an axis positioned at one end of said table portion, said axis being located with respect to the surface of said table portion whereby at least a portion of said first roll extends below said surface, said first roll having a cross sectional area at the center of its longitudinal length greater than at the ends thereof, a track structure located on a side of said table portion opposite said first roll, said track structure extending in a direction perpendicular to the axis of said first roll, a carriage freely movable along said track structure, a second roll mounted on said carriage and rotatable about an axis which is substantially parallel to said first-mentioned axis, the axis of said second roll being located with respect to the surface of said table whereby at least a portion of said second roll extends below said surface, said second roll also having a cross sectional area greater at the center of its longitudinal length than at the ends thereof to match the cross sectional area of said first roll, a stop for limiting movement of said carriage toward said first roll, means on the outer peripheries of said first and second rolls for clamping the opposite ends of a workpiece positioned on said flat table portion, and means for rotating said rolls in opposite directions whereby said freely movable carriage is forced to traverse said track structure until it engages said stop, whereupon the workpiece will be elevated to a position where its plane is tangential to the peripheries of said rolls and further rotation of at least one of said rolls will cause stretching in said workpiece.

6. A stretcher for flat workpieces comprising, in combination, a base member having a substantially fiat table portion, a first roll rotatable about an axis positioned at one end of said table portion, a track structure located at the opposite end of said table portion and below the surface thereof, said track structure extending in a direction substantially perpendicular to the axis of said first roll, a stop member at the end of said track structure adjacent said table portion, a carriage freely movable on said track structure from a position outwardly of said table portion to a position in close proximity to said table portion where it abuts said stop member, a second roll mounted on said carriage and rotatable about an axis which is substantially parallel to said first-mentioned axis, means on the outer peripheries of said rolls and extending along the longitudinal length thereof for clamping the opposite ends of a flat workpiece positioned on said table portion while said carriage is in its position outwardly of the table portion, means for rotating said first roll through 90 degrees after the said opposite ends are clamped, means for locking said first roll after it has rotated through 90 degrees, and means for rotating said second roll in a direction opposite to the direction of said first roll whereby said carriage is forced to traverse said track structure toward the table portion while the workpiece is lifted to a position where its plane is tangential to the peripheries of said rolls, said movement of the carriage toward the table portion continuing until it engages said stop member, whereupon further rotation of at least one of said rolls will cause stretching in said workpiece.

References Cited in the file of this patent UNITED STATES PATENTS 823,766 Conklin June 19, 1906 1,688,252 Tytus Oct. 16, 1928 1,829,339 Corrigan Oct. 27, 1931 2,084,148 Lamb June 15, 1937 2,289,161 Zalkind July 7, 1942 2,716,688 Lackner Aug. 30, 1955 

